A Study of e⁺e⁻ Annihilation into Hadrons in the 1400–2200 MeV Energy Range with the Magnetic Detector DM1 at DCI: Observation and Study of a φ′ Vector Meson

Abstract

The e⁺e^- annihilation into hadrons has been studied for $1.4\, < \,\sqrt {\text{S}} \, < \,2.2$ GeV. The total integrated luminosity was 1500 nb^-1 over the whole energy range. Accurate magnetic analysis of charged particle momenta allowed a constrained kinematical reconstruction of events with at most one neutral missing.

Cross-sections are given for production of the following exclusive channels: π⁺π⁺π⁻π⁻ (including ρº π⁺π⁻), π⁺π⁺π⁻π⁻πº (including ωπ⁺π⁻), K⁺K⁻ ${\text{K}}_{\text{S}}^{\text{o}}{\text{K}}_{\text{L}}^{\text{o}},{\mkern 1mu} {\text{K}}_{\text{S}}^{\text{o}}{K^\pm }{\pi ^ \mp }$ (including ρº π⁺π⁻), π⁺π⁺π⁻π⁻πº (including ωπ⁺π⁻), K⁺K⁻, K ^o_S K ^o_L , ^o_S K^± (including K*Kπ). The inclusive result concerns the production of ${\text{K}}_{\text{S}}^{\text{o}}$.

The ρ′ (1.55) is observed in the 4 π^± channel with high statictics. A small bump in the ωπ⁺π⁻ channel is observed near 1.65 GeV with a height 6.7 standard deviation above background. The rather high cross-section $K\bar K\pi$ production in the same region and the dynamics of this channel, exhibiting an I = 0, I = 1 interference, show that this bump is due to a new φ’ vector meson rather than to an ω′. This new φ′ (1.65 GeV) has a 150 MeV width and decays mainly in KK*.

Work supported by ther “Institut National de Physique Nucléaire et de Physique des Particules”